As rules of environmental protection become more and more strict, Europe enforced Euro II Standard in 1996, Euro III Standard in 2000, and Euro IV Standard in 2005, i.e. sulfur in gasoline must reach up to 10 ppm; in American Tier 2 Standard, sulfur in gasoline is required less than 300 ppm in 2004, and less than 30 ppm in 2005; Asia, Bangkok Thailand, Delhi India and Korea enforced Euro II Standard or standard equal to Euro II Standard successively in 1999 and 2000; Japan enforced more strict standards than Europe with keeping pace with America. Beijing, China enforced Euro II Standard in Jul. 1, 2000, and Euro III Standard in 2005, and aimed to get the vehicle emission standard keep pace with Europe in 2010. Therefore, there is an urgent need to develop a process technology meeting the standard of low-sulfur gasoline.
Since more than 90% of sulfur and more than 90% of olefin in final gasoline are originated from FCC gasoline, it would be paid continuous attention to the quality of FCC gasoline. Currently, the processes of reducing sulfur content in FCC gasoline can be generally divided into three types: removing sulfur in FCC feed oil (pre-hydrotreating process); producing low-sulfur gasoline directly in FCC process; post-treating FCC gasoline.
Pre-hydrotreating of FCC feedstock is an efficient process to reduce sulfur content in gasoline. For example, CN1351131A discloses a process for treating S-containing crude oil comprising combining ordinary-pressure or vacuum distillation, coking or removing asphalt with solvent, medium-pressure hydrocracking and catalyst cracking, so that high-sulfur feed oil with 1.8-2.8% of sulfur can be treated by refinery factory. However, according to the such process, saturation degree of olefin is increased and octane number of gasoline is decreased, and thereby the hydrotreating process requires a great investment and high operation cost.
Currently, various post-treating process of FCC gasoline was developed overseas. For example, ISAL process developed jointly by INTERVEP and UOP, which mainly used to solve the problems of octane number and sulfur content in post-treatment of FCC gasoline. The octane number of gasoline obtained through the ISAL process is higher by 7.4 units than that of ordinary hydrotreating gasoline (road octane number), which meets the requirement of 25 ppm sulfur and of maintaining octane number of gasoline in the refinery factory.
The S-Zorb gasoline desulfurization (SRT) process developed by Phillips Petroleum Company can obtain environmentally friendly gasoline products with minimum lost of octane number and low consumption of hydrogen.
CN1485414A discloses a process for non-hydroaromatizating and desulfurizing catalytically cracking for gasoline, comprising making full-cut of FCC gasoline or light fraction after the fraction being flowed into an aromatizing desulfurizing reactor for aromatization reaction for olefin, performing hydrodesulfurization reaction with the hydrogen produced from aromatization reaction, reducing olefin and sulfur contents in gasoline.
Other post-treating desulfurizing technologies for industrialized gasoline include: SCANfining process jointly developed by Exxon and Akzo; Prime-G+ process of gasoline ultra-deep desulfurization developed by France Petroleum Research Institute, with sulfur content in the obtained gasoline of less than 50 μg/g and desulfurization rate of 97.5%; and ROK-Finer process developed by Japanese Petroleum Company, putting into operation in 2004 with sulfur in the produced gasoline of less than 10 μg/g. Although the post-treating desulfurizing technologies of gasoline has relatively high desulfurization rate, it still needs new devices with increasing device investment.
Directly reducing sulfur content in gasoline during catalytic cracking process mainly commence on catalyst and process. Regarding technology of using sulfur reduction catalyst or the additives, the sulfur reduction additive of GSR series and D-Prism series developed by Grace Davison Company (U.S. Pat. No. 5,376,608) with aluminum oxide/titanium oxide as matrix, supporting L-acid components such as zinc oxide, can be used to reduce sulfur content in FCC gasoline by about 20%-35%; FCC catalyst of SATURN developed by Grace Davison Company can be proved to reduce sulfur content in FCC gasoline by above 50% in industrial test.
With regard to the technology of RESOLVE series additives developed by Akzo Nobel Company, RESOLVE 700 can be used to reduce sulfur content in gasoline of from 600 μg/g to 442 μg/g when processing non-hydrotreating VGO feedstock containing 0.7% of sulfur. The sulfur content in gasoline of full-cut range continues to fall from 442 μg/g to 340 μg/g after adding 10% of RESOLVE 800. Sulfur reduction is carried out by using the sulfur reduction catalyst of NaphthaMaz-LSG developed by Engelhard Company on the basis of NaphthaMax catalyst with high conversion rate and gasoline yield.
Regarding the process technology of reducing sulfur content in gasoline directly during catalytic cracking process, U.S. Pat. No. 6,287,522 B1 refers to LOCC process by using a catalytic cracking device with dual-riser reactor, comprising transporting the mixed spent catalysts consisting of the most non-stripping spent catalyst from a light hydrocarbon riser reactor and a small amount of non-stripping spent catalyst from a heavy oil riser reactor to the bottom of the heavy oil riser reactor through a catalyst delivery pipe, then mixing with a high temperature regenerative catalyst from a regenerator, and then the mixed catalysts go upwards in the heavy oil riser reactor, contacting and reacting with the feeds in the heavy oil riser reactor. The temperature of the catalyst, which is contacted with the feed of heavy oil riser reactor is decreased by using such process, with taking advantage of higher activity and lower temperature of the spent catalyst in the light hydrocarbon riser reactor, reducing thermal cracking reaction of the heavy oil riser reactor, promoting the catalytic cracking reactor, and improving the products distribution. However, the self-recycling catalyst of such process is not conveyed to the light hydrocarbon riser reactor, causing low ratio of catalyst of light hydrocarbon riser reactor to gasoline feed and short reaction time, thus it is too poor to the gasoline desulfurization.
CN1401740A discloses a catalytic converting process for upgrading poor-quality gasoline, including a conventional catalytic cracking step for the heavy oil and a catalytic converting step for upgrading the poor-quality gasoline. It is characterized in that a common catalyst regenerator and a same FCC catalyst are used in both steps. In such process, sulfur content is decreased 15-50 percentage points and octane number of gasoline is increased 0.2-2 units.
CN1176189C discloses a catalytic converting process for upgrading poor-quality gasoline and the device thereof, comprising applying a dual-riser (a heavy oil riser reactor and a gasoline riser reactor) catalytic cracking process and the conventional catalytic cracking catalyst to upgrade the poor-quality gasoline. Desulfurization is realized by conversion of sulfide in gasoline and hydrogen transfer reaction, of which sulfur content in gasoline reduced by 5-30 wt %, resulting the decreased level of sulfur content being limited.
CN1721055 discloses a dual riser catalytic cracking device for decreasing sulfur content in catalytic cracking gasoline, which is used to solve the high sulfur content problem in catalytic cracking gasoline present in the existing conventional catalytic cracking device. The above device comprises a heavy oil riser reactor and a gasoline riser reactor, in which an expanding-structural cylinder layer-shape reactor is put on the vertical stand pipe below the raised air inlet of the gasoline riser reactor; pre-rise medium inlet is put on vertical stand pipe below the layer-shape reactor. By using desulfurization catalytic cracking catalyst, the sulfur content can be decreased by 50-70%, the olefin content can be decreased by 20-40 vol %, and the octane number of gasoline (RON) can be increased by 0.3-2.0 units. The layer-shape reactor of the such device has a reaction temperature of 630-720° C., a reaction pressure of 0.15-0.45 Mpa, a catalyst retention time of 30-200 seconds, and contains a gasoline riser reactor simultaneously. By taking advantage of the layer-shape reactor and the gasoline riser reactor, such process can be used to reduce gasoline content in gasoline greatly. however, the regenerated high temperature catalyst directly flows into the heavy oil riser reactor and the layer-shape reactor without cooling to contact and react with hydrocarbon, causing the catalyst coke immediately and the quality of products is unstable, which is not easily operated and controlled. Otherwise, the layer-shape reactor has high operation temperature with unfavorable to upgrade gasoline and having low yield of gasoline.
CN1861757 relates to a catalytic cracking process for high efficiency decreasing sulfur content in gasoline and the device thereof. In such process, one or more oxidation-reduction treating units are added into the reactor-regenerator system of the existing riser of catalytic cracking device. Under certain reaction conditions and atmosphere, they are contacted with the cycling liquid FCC catalyst to generate oxidation-reduction reaction for adjusting the valence of metal component in the catalyst and meeting the demand of the desulfurizing activity in order to maintain the desulfurizing activity on a high level. Another riser having treatment unit is further added into the reactor-regenerator system to contact the catalytic cracking gasoline with the compound of the catalyst treated by high temperature so as to conduct second cracking reaction, achieving the purposes of desulfurization, decreasing olefin content, and increasing octane number in gasoline. according to such process and the selection of some certain catalysts, the sulfur content in FCC gasoline can be decreased to more than 80% and olefin to 10-25 (v) %, and the research octane number in gasoline cannot be decreased but increased a little.
CN101104815A and CN200610048408.1 relate to the modification of the gasoline riser of existing double riser catalytic cracking device, comprising two kinds of processes: providing a rapid bed reactor on the top of the gasoline riser reactor, or replacing the gasoline riser directly with the rapid bed reactor. Though the modification of gasoline is realized by both the processes, some of regenerated catalysts would flow into the rapid bed reactor to go on reacting. As the reaction goes on, carbon increasingly deposits on the catalyst, resulting in unstable quality of upgraded products of gasoline. The catalyst flowing into the gasoline upgrading reactor does not permit an efficient decreasing temperature treatment, making the temperature of gasoline upgrading reaction uneasily controlled efficiently, also resulting in unstable quality of upgraded products of gasoline.
CN1245202A relates to a novel riser reactor and a hybrid reactor composed of a riser and a fluidized bed, applying two-region reaction to supply favorable conditions for catalytic cracking hydrogen transfer reaction: low temperature and long residence time. Due to pressure balance problem of the catalytic cracking device, highly dense phase bed layer surface cannot be formed either in middle or top portion of the riser. Therefore, an ideal effect cannot be obtained from the hydrogen transfer reaction of the process in industrial implement.
In order to adjust the severity of the reaction in the riser properly when strengthening conversion level of feedstock, CN1206036 discloses a scheme of the cooling regenerated catalyst, i.e. cooling some of the regenerated catalyst. The cooled regenerated catalyst is admixed with non-cooled high temperature regenerated catalyst in pre-lift zone of riser, and flows upward in the presence of pre-lift medium to contact and react with feed oil in reaction zone. The restriction of thermal balance of catalyst is broken down by means that the catalyst cooled, making its convenient to adjust ratio of the catalyst to the oil during the reaction, strengthening the conversion ability of the heavy oil, and improving the products distribution. However, the matter of high olefin content in gasoline is not solved and the effect of sulfur reduction is not realized.
CN1200083C relates to a catalytic cracking combination process including the following steps: cooling 10-80 wt % of the regenerative agent, following by feeding it into the reaction zone of a circulating fluidized bed reactor to contact and react with the gasoline to obtain a reaction oil-gas; then feeding the resulting reaction oil-gas into the subsequent gasoline conversion product separation system and feeding the reacted catalyst into the stripper zone of the circulating fluidized bed reactor to strip; recycling 40-90 wt % of the stripped catalyst into the reaction zone for circulating use and feeding the residual portion into a riser reactor and making it mix with non-cooled regenerative agent and flow upward along the riser reactor in presence of pre-lift medium; injecting the hydrocarbon raw material into riser and making it contact and react with the catalyst, and making reactant flow through the riser outlet and come into a settler; making the oil-gas and the catalyst isolated react, and feeding the oil-gas into the subsequent product separation system, and putting the reacted carbon-deposited catalyst into recycling use after stripping and regeneration. Through the process, the conversion ability of the heavy oil and the quality of the product has been improved. However, as the reaction goes on, carbon deposits increasingly on the catalyst in the circulating fluidized bed reactor, influencing the property of upgraded gasoline product, thus the quality of the product is unstable, and desulfurization cannot be realized to a maximum extent. Regenerated catalyst has high temperature so as to make it easy to coke when contacting with feed oil after flowing into the riser reactor. The operation of the process is unsteady with quality of product unguaranteed.
CN02149314.6 relates to a process of upgrading catalytic gasoline for olefin reduction and the device thereof, comprising feeding the spent catalyst having high activity and low temperature which is through upgrading of catalytic gasoline into a new-added mixing vessel of the catalyst, also introducing the high temperature regenerated catalyst from the original regenerator, and introducing unreacted catalyst which needs to be replaced in the original catalytic cracking device, resulting in that three catalyst flows are admixed under the fluidization of fluidized air from the bottom of the mixing vessel of catalyst, with coke burning reacted. The gasoline upgrading reactor is selected from the group consisting of riser reactor, turbulent bed reactor and rapid bed reactor. The purposes of reducing olefin content and increasing octane number are achieved by such process, but, since coke burning of catalyst is carried out at a temperature of above 600° C., the temperature of the catalyst after coke burning in the mixing vessel cannot be efficiently decreased; it is not sure that the catalysts flowing into the gasoline upgrading reactor are all low temperature catalysts. If high temperature catalyst flows into gasoline upgrading reactor, upgrading of gasoline would be easily overcracking with selectivity of products unstable. The high temperature catalyst flowing into the heavy oil riser reactor would be easily coked. Furthermore, in addition that three catalyst flows are admixed for use, the operation of the process is not easily controlled and the quality of the products is unstable.
The reactors of all the above applications and/or patents are dual riser or hybrid reactor, wherein, some of them not only increase additional reactor units for reduction treatment of the catalytic active components or high temperature (600-700° C.) pre-reaction of the gasoline, but also increase the equipment investment and the process procedures, resulting in the gasoline yield decreasing; the others apply partial regeneration to obtain the regenerated high temperature catalyst, which is not cooled, resulting in bad selectivity of the products and unstable operation.